The present invention relates in general to heat recovery steam generators and, in particular, to a new and useful assembly for the shipping and support of modules for heat recovery steam generators.
As shown in FIG. 1, a heat recovery steam generator, generally designated 5, comprises an inlet flue 7 and pressure parts or heat recovery surfaces 15 which are contained inside a box-type structure comprised of cold outer casing or plate material 10 that is internally insulated and lined. The cold outer casing 10 is internally insulated with an insulation layer 34 and lined with a liner 36 as shown in FIG. 6. The cold outer casing 10 is supported by an external support frame 2.
Returning to FIG. 1, high temperature turbine exhaust gas passes through the heat recovery steam generator 5, entering a front end or inlet 7 of the heat recovery steam generator 5. The temperature of the turbine exhaust gas at this point can easily exceed 1000.degree. F. Heat which is given off from the hot turbine exhaust gas is recovered by a working fluid flowing through the pressure parts 15 located within the heat recovery steam generator 5. The heat recovery surfaces 15 are located in modules 12 contained within the casing 10. The turbine exhaust gas passes across the modules 12 to an outlet transition housing 9 which leads to a stack 11 for the exiting of the exhaust gas. At the stack 11, the temperature of the turbine exhaust gas has been reduced to approximately to 200.degree. F.
Because of economic considerations, it is common practice in the heat recovery steam generator field to employ modules 12 which are pre-fabricated and pre-assembled in a shop. Modular design minimizes the amount of field assembly and labor by maximizing the amount of work done in the controlled environment of the manufacturing facility. Once shipped to the field, the modules 12 are field assembled and arranged side-by-side to create the heat recovery steam generator 5. Large heat recovery steam generators 5 can be two or more modules 12 wide.
The cold outer casing 10, insulation layer 34 and liner 36 form panels in what is known as a cold casing design. As illustrated in FIG. 6, these casing panels 10 are usually installed after the modules 12 have been positioned in the field. The casing panels 10 provide the overall strength and stability for the heat recovery steam generator 5 by providing side-to-side as well as fore and aft restraints against potential loadings which can occur as a result of wind and/or seismic conditions.
The pressure parts 15 comprise the most significant portion of the total weight of each module 12 and must be externally supported and restrained by structural tie members 38 for both shipping and erecting purposes. It is common in the heat recovery steam generator field to employ modules 12 having structural shapes comprising wide flanges, channels, and angles for achieving the transportation and construction of the generator 5.
The large sizes required for these types of structural members directly impact the maximum number of pressure parts 15 which can be shipped in a single module 12 due to overall shipping width and weight restrictions. Specifically, the width dimensions for shipping a given module 12 must be less than the allowable clearances specified by regulations for both vehicle and rail transportation. The number of pressure parts 15 which can be shipped in a module 12 is thus a function of the allowable shipping width clearance minus the maximum width of the attached shipping steel side truss members.
Moreover, the number of shippable pressure parts 15 which can be incorporated into a given module 12 is also a function of the maximum permissible shipping weight minus the weight of the shipping steel members used for shipping. In order to stay within the maximum permitted shipping weight, the weight of the shippable pressure parts 15 must be reduced by an amount corresponding to the weight of the shipping steel. Therefore, the heavier the shipping steel, the less the amount of pressure parts 15 which can be incorporated and shipped in a given module 12.
Previous heat recovery steam generator designs have required significant field labor for shipping and erecting. Additionally, in these previous designs, much of the steel that is required for shipping the modules 12 must be removed and discarded after the modules 12 have been erected, resulting in additional expense and waste.
Referring to FIG. 6, the pressure parts 15 of the modules 12 are laterally restrained at several locations along the length of the module 12 by intermediate ties 37. Intermediate ties 37 restrain and support the load of the module 12 during shipment. The ties 37 also prevent buckling and excessive vibration of the pressure parts 15 during operating conditions once the modules 12 have been assembled into the heat recovery steam generator 5.
As illustrated in FIG. 6, for single module 12 wide heat recovery steam generator designs, the intermediate tie steel members 37 penetrate the internal liner 36 and the insulation 34 for support from the cold outer casing 10 and the support frame steel 2. This configuration for the intermediate ties 37 is widely used in known designs. Because of this design, the size of the intermediate ties 37 must be small enough so that the flow of turbine exhaust gas through the modules 12 is not significantly altered or obstructed. In heat recovery steam generators 5 (FIG. 1) that have more than one module 12, the length of the intermediate tie support steel 37 must be significantly increased. The increase in the intermediate tie steel 37 is impractical due to the combination of longer spans, elevated temperatures, and minimum size requirements associated with support steel located in the gas stream.
For multiple module 12 wide designs, a current solution to this problem is to use intermediate tie members 37 that are integral with the pressure parts (i.e., spirally finned tubes) 15. The intermediate tie steel members 37 are welded to the fins on the spirally finned tubes 15 in order to support the tie steel members 37. Because of this configuration, however, the support attachments of tie steel members 37 are prone to failure due to temperature differentials between the tubes, the fins of the heat recovery surfaces 15, and the intermediate tie steel members 37. Additionally, some failures in this design can also be attributed to a lack of well-defined supports and load paths that could accommodate the high design temperatures and loadings of the intermediate tie steel 37 during unit operation.
Currently, there are no known designs which exist that provide for an efficient handling and shipping of a module for a heat recovery steam generator while providing for efficient support during the operation of the unit.